Thomas Reimer

Transpiration Cooling Tests of Porous CMC in Hypersonic Flow

During hypersonic flight the temperatures on the vehicle can reach very high values in certain locations. A hypersonic flight vehicle needs to be designed aerodynamically efficient. That results in rather small nose and leading edge radii which drives up thermal loads due to the fact that the loads depend on the curvature radius of these elements. Therefore thermal protections is required for these elements. However, even ceramics reach their use temperature limits when e.g. the leading edge radius of a space plane is in the order of only a few centimeters. Transpiration cooling could be a means to handle the thermal loads in certain critical locations for a hypersonic flight vehicle. This paper describes the loads derived for a conceptual space plane vehicle, the SpaceLiner, and also reports on the initial tests for transpiration cooling of ceramic matrix composites in the hypersonic flow of an arc jet facility.

System Studies on Active Thermal Protection of a Hypersonic Suborbital Passenger Transport Vehicle

Aerodynamic heating is a critical design aspect for the development of reusable hypersonic transport and reentry vehicles. The reliability in terms of thermal resistance is one of the major driving factors with respect to the design margins, the mass balance and finally the total costs of a configuration. Potential designs of active cooling systems for critical regions such as the vehicle nose and leading edges are presented as well as preliminary approaches for their impact on the total mass. The visionary suborbital passenger transport concept SpaceLiner is taken as a reference vehicle for these studies. Covering the whole flight regime from subsonic to Mach numbers of more than 20, this vehicle creates high demands on the thermal protection system. Part of the work was performed within the DLR research project THERMAS.

OVERVIEW ABOUT THE INSTRUMENTED NOSE ASSEMBLY DEVELOPMENT FOR THE EXPERT CAPSULE

The EXPERT mission aims at collecting precise in-flight data during atmospheric re-entry. For this purpose a vehicle was envisaged that is designed especially for that. Almost twenty payloads are on board of the EXPERT capsule which has the shape of a cone with a blunt nose. Four non-moveable flaps are located at the end of the capsule. The nose of the vehicle is made from a ceramic matrix (CMC) composite material. In the nose four exciting experiments are situated. Payload 1 is a Flush Air Data System that measures the pressure and the heat flux in five positions on the nose. Payload 2 collects temperature date on the inside of the ceramic nose at six locations via pyrometric measurements. Payload 10 is a spectrometer that investigates the chemical properties of the boundary layer around the nose via an optical window in the nose. Palyoad 11 is an experiment that deals with the catalycity of materials in the region of the interface of the nose to the adjacent metallic Thermal Protection System (TPS) of the capsule. This paper describes the development of the Instrumented Nose Assembly of the EXPERT capsule, referred to as the NAP, from the design concepts over the analysis and the tests up the flight hardware assembly.

Reentry Flight Testing of a C/C-SiC Structure with Yttrium Silicate Oxidation Protection

Hot structure design with ceramic matrix composites (CMC) which are based on carbon fiber reinforced materials like C/C-SiC is a key technology for the development of lightweight thermal protection systems (TPS) of advanced space reentry vehicles. In order to select suitable CMC and protective coating materials, ground based hypersonic flight simulation with plasma wind tunnel test facilities represents a valuable method for qualifying several structure components and to achieve a deeper understanding of the thermo-chemical interactions at the material’s surface. However, regarding the technical limitations with ground based test facilities it is indispensable to perform real flight testing with CMC structures in terms of validation of new design concepts which are based on innovative materials. This paper describes a reentry technology experiment – named “KERAMIK” – with its structural components designed and manufactured fully in C/CSiC material, a special type of CMC developed by DLR. It was successfully flown on the Russian Foton-M2 mission in June 2005. One of its C/C-SiC panels was partly protected with different coating. Special attention is paid to an effective two-layer coating system that is based on yttrium silicate and was chosen to improve both oxidation protection and erosion resistance of the C/C-SiC material. Before selected for the flight test, this coating system was extensively tested in plasma wind tunnel facilities. A comparison of the test results with such coated C/C-SiC specimens obtained from test campaigns in different plasma wind tunnel facilities shows two principal approaches for systematic ground based reentry qualification tests.

Lifetime Testing of a CMC TPS under Vibration Load

A ceramic matrix composite thermal protection system test article was subjected to a dynamic load environment to determine its lifetime. The test article consisted of one panel made from the ceramic matrix composite and the corresponding structural items to mount on a substructure. Special attention was given to the fasteners which were also designed and made from the ceramic matrix composite. An elastic foam material was included between panel and carrier structure which is representative of a flexible high-temperature insulation. The setup is representative of the design that was developed for re-entry vehicles like the SHEFEX I and II flight experiments. A mechanical random vibration load was defined typical of the acoustic loads present around a hypersonic flight vehicle in a turbulent boundary layer. The tests were carried out on a shaker in one direction perpendicular to the panel surface. A total test time of 100 hours was accumulated without noticeable degradation of the fastener performance or the other test items.

Arc Jet Testing of CMC Samples with Transpiration Cooling

High speed sustained atmospheric flight creates high thermal loads at the tip, leading edges, intake ramps or engine structures of a flight vehicle. However, sharp edges are mandatory for these vehicles in order to obtain the required aerodynamic performance. To provide technical solutions for these problems, the concept of using porous ceramic matrix composite (CMC) materials in combination with active cooling by transpiration was investigated. An arc jet test campaign was carried out to determine basic parameters in terms of minimum required coolant focusing on liquid water as the coolant media. The tests were stagnation tests on flat samples with a diameter of 50 mm. The front wall thickness was 8 mm. The tests were carried out in the L3K and L2K arc jet facilities of DLR Cologne at approximately 1 MW/m² heat load. Good results were achieved in terms of mass flow data for C/C samples. A number of tests could be carried out at low supply pressures and low mass flow. A medium value of the lower limit mass flow is 0.33 g/s at a pressure of 225 hPa which is equal to 0.152 kg/m²s. With aluminum oxide samples, a cold surface could also be maintained, however, it was not possible to establish a steady-state condition in terms of mass flow and supply pressure.